When the accelerator is released, the throttle return spring in the accelerator linkage closes the throttle plates simultaneously with the release of the release of the pedal. As the throttle plates approach the closed position, the head of the dashpot adjusting screw in the end of the throttle lever contacts the end of the dashpot diaphragm rod. As the diaphragm rod is pushed in, the diaphragm forces air out the air passage in the dashpot mounting screw, or around stem or units that have valve in diaphragm. Because of the restriction in the tip of this air passage, the inward movement of the diaphragm and disphragm rod is retarded and allows the rod to compress the return spring only slowly. This, in turn, retards the clsoing rate of the throttle plates enough to permit the engine to dissipate the raw fuel and prevent stalling from an over-rich mixture.